DEAR DOCTOR K: I endured some physical and emotional abuse as a child. Could this explain why I struggle with anxiety as an adult?

DEAR READER: Sigmund Freud and many other psychiatrists surely thought so. Indeed, exploring the experiences of childhood is an important part of psychoanalysis.

This view did not think that childhood experiences could actually make physical changes in brain chemistry, however. Instead, it imagined an unchanged brain that simply was given unusually difficult experiences to cope with.

Today, we have a somewhat different view. We now know that childhood is a time when the brain is exceptionally fragile and vulnerable to outside influences. Exposure to extreme stress — for example, abuse, neglect, violence in the home or the loss of a loved one — can affect a child’s developing brain. It can impair his or her ability to negotiate emotional bumps in the road later on. Scientists call this toxic stress.

Studies show that toddlers who live in unstable families have a strong stress response when confronted with a new and unexpected situation. On the other hand, children from healthy families are better able to weather unknown situations.

Psychological and physical trauma in childhood seems to alter the brain in a way that makes it more susceptible to anxiety. For one thing, it makes what is known as the HPA axis overly sensitive. The HPA axis is a pathway of hormones that influence mood. Imbalances of certain hormones in this pathway increase the risk for anxiety and may induce anxiety symptoms.

Early trauma may also cause a lasting increase in certain stress hormones, and the pumped-up levels of these hormones may keep the body in a state of alert. (I’ve put an illustration of this on my website, AskDoctorK.com.)

Traumas may also change the structure of the brain. The hippocampus is a part of the brain that plays a central role in processing long-term memories. It works closely with the amygdala, the brain’s “fear” center. The hippocampus is smaller in some people with post-traumatic stress disorder. It is also smaller in some people who have endured extreme, prolonged stress.

Of course, not everyone who has survived a traumatic event develops an anxiety disorder. That’s where a person’s genes and brain chemistry come in. It’s possible that some people are genetically or biologically more susceptible to anxiety, but it may take a traumatic life event to actually “push” them into being anxious.

In fact, an inherited tendency to be anxious may actually turn some childhood experiences into traumatic ones. For example, it may cause a 3-year-old to fear she has been abandoned every morning when her parents leave for work. Most 3-year-olds without that inherited tendency would not feel abandoned.

On the other hand, trauma is not always a trigger. Some people who develop an anxiety disorder have not endured particularly stressful events. As with most illnesses, anxiety is affected both by genes and by life experiences.